Feed pretreating

ABSTRACT

This invention provides for a process for hydrocarbon conversion in which a partially dehydrated hydrocarbon feedstock is contacted with at least two different molecular sieve materials, including a first molecular sieve having a Si/Al molar ratio of less than about 5 and a second molecular sieve having a Si/Al molar ratio of greater than about 5. Also, this invention includes such processes in which such feedstocks are contacted with a first molecular sieve having pores of at least about 6 Angstroms and a second molecular sieve having pores of less than about 6 Angstroms.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/807,777 filed Mar. 22, 2004 now abandoned, which applicationis a nonprovisional application that claims the benefits of U.S.provisional patent application Ser. No. 60/457,087 filed Mar. 24, 2003.

FIELD OF THE INVENTION

The present invention relates to a process for removing substances froma chemical feedstock prior to catalytic conversion in which the catalystwould be impaired by such substances. In particular this inventionprovides a process for extending the life of catalysts useful foralkylation of aromatics both between regeneration cycles and untilreplacement is required.

BACKGROUND OF THE INVENTION

Hydrocarbon conversion processes using catalysts are often subject tocatalyst regeneration and replacement requirements resulting from“poisoning” of the catalyst by one or more impurities contained in thehydrocarbon feedstock. In many cases, catalyst developments, e.g. toreduce coke-forming and other by-product reactions, have progressed tothe stage where “poisoning” by feedstock impurities is the primaryreason that catalyst performance deteriorates which forces the catalystto be replaced or regenerated. Various processes have been developed forremoval of such impurities prior to contact with the catalyst.

Alkyl aromatic compounds such as cumene and ethylbenzene are oftenproduced by reaction of aromatics and olefins in the presence of acidicmolecular sieve catalysts. Liquid phase operation of aromaticsalkylation processes has often been found to result in reduced operatingcosts as well as fewer undesirable byproducts than earlier vapor phasetechnologies.

Catalysts that can be used for alkylation of benzene with propylene andalso for transalkylation of benzene and polyisopropylbenzenes in liquidphase include zeolite beta, zeolite Y, zeolite omega, ZSM-5, ZSM-12,ITQ-1, ITQ-2, ERB-3, SSZ-25, MCM-22, MCM-36, MCM-49, MCM-56, MCM-58,MCM-68, faujasite, mordenite, porous crystalline magnesium silicates,and tungstate modified zirconia, all of which are known in the art.

Catalysts that can be used for alkylation of benzene with ethylene andtransalkylation of benzene and polyethylbenzenes in liquid phaseprocesses include zeolite beta, zeolite Y, zeolite omega, ZSM-5, ZSM-12,ITQ-1, ITQ-2, ERB-3, SSZ-25, MCM-22, MCM-36, MCM-49, MCM-56, MCM-58,MCM-68, faujasite, mordenite, porous crystalline magnesium silicates,and tungstate modified zirconia.

Operation of aromatics alkylation reactions in the liquid phase,especially at relatively low temperatures, has resulted in greatercatalyst sensitivity to trace impurities in the feedstock. Variousefforts have been made to reduce impurities to extend the catalyst life.Impurities often result in both more frequent catalyst regenerationrequirements and reduced ultimate life of the catalyst beforereplacement is necessary. Catalyst replacement often involves a processshutdown, lost production, and significant costs. A variety of processeshave been developed for pretreating chemical feedstocks to removeharmful impurities. These processes include distillation, adsorption,and extraction.

U.S. Pat. No. 6,313,362 (Green), which is incorporated herein byreference, teaches an aromatic alkylation process in which thealkylation product is contacted with a large pore molecular sievecatalyst such as MCM-22 in a liquid phase step to remove impuritiesprior to liquid phase alkylation. Impurities taught as being removedinclude olefins, diolefins, styrene, oxygenated organic compounds,sulfur-containing compounds, nitrogen-containing compounds, andoligomeric compounds.

U.S. Pat. No. 4,358,362 (Smith), which is incorporated herein byreference, teaches a method for enhancing catalytic activity of azeolite catalyst by contacting a feed stream which contains acatalytically deleterious impurity with a zeolitic sorbent. Thisinvention uses a sorbent with a Si/Al ratio greater than 12,10–12-membered rings, and a Constraint Index between 1 and 12,preferably ZSM-11.

U.S. Pat. No. 5,030,786 (Shamshoum), which is incorporated herein byreference, teaches a process for production of ethylbenzene in which thecatalyst lifetime is increased by reducing the concentration of water inthe feed to the reactor.

U.S. Pat. No. 5,744,686 (Gajda), which is incorporated herein byreference, teaches a process for the removal of nitrogen compounds froman aromatic hydrocarbon stream by contacting the stream with a selectiveadsorbent having an average pore size less than about 5.5 Angstroms. Theselective adsorbent is a non-acidic molecular sieve selected from thegroup consisting of pore closed zeolite 4A, zeolite 4A, zeolite 5A,silicalite, F-silicalite, ZSM-5, and mixtures thereof.

A process for preparing alkylated benzenes is taught in U.S. Pat. No.6,297,417 (Samson), which is incorporated herein by reference. Theprocess includes contacting a benzene feedstock with a solid acid, suchas acidic clay or acidic zeolite, in a pretreatment zone at atemperature between about 130° C. and about 300° C. to improve thelifetime of the alkylation and transalkylation catalyst.

U.S. Pat. No. 6,355,851 (Wu), which is incorporated herein by reference,teaches a zeolite-catalyzed cumene synthesis process in which benzenefeedstock is contacted with a “hot” clay bed, followed by distillationof the benzene feedstock to separate the benzene from the highermolecular weight materials formed from olefinic poisons during the hotclay treatment, followed by a “cold” clay treatment wherein the benzenedistillate is contacted with an ambient-temperature clay. The propylenefeedstock is pretreated by contact with an alumina to remove tracesodium compounds and moisture, a molecular sieve to remove water, andtwo modified aluminas to remove other catalyst poisons. The pretreatedpropylene and benzene feedstocks are then reacted in the presence of azeolite catalyst to form cumene without causing rapid degradation of thecatalyst's activity.

PCT published application WO0214240 (Venkat), which is incorporatedherein by reference, teaches removal of polar contaminants in anaromatic feedstock by contacting it with molecular sieves with pore sizegreater than 5.6 Angstroms at temperatures below 130° C.

While the processes described above are often successful in improvingthe life of molecular sieve catalysts, catalyst life is still a problemin commercial applications. The limitations and deficiencies of theseprior art techniques are overcome in whole or at least in part by theprocess of this invention.

SUMMARY OF THE INVENTION

This invention provides for a process for hydrocarbon conversion inwhich a hydrocarbon feedstock is contacted with at least two differentmolecular sieves to produce a treated hydrocarbon feedstock. Preferably,the first molecular sieve has a Si/Al molar ratio of less than about 5and a second molecular sieve has a Si/Al molar ratio of greater thanabout 5. In another embodiment, such hydrocarbon conversion processincludes contacting a hydrocarbon feedstock with at least a firstmolecular sieve and a second molecular sieve, wherein the first andsecond molecular sieve have different pore diameters, to produce atreated hydrocarbon feedstock. Preferably, the first molecular sieve hasa pore diameter of at least about 6 Angstroms and the second molecularsieve has a pore diameter of less than about 6 Angstroms.

In yet another embodiment, the invention is directed to a process foralkylation of an aromatic hydrocarbon using an aromatic feedstock whichhas been pretreated using the process described above.

In still yet another embodiment, the invention is directed to a processfor alkylation of aromatics using an alkylating agent and an aromatichydrocarbon which both have been pretreated using the process describedabove.

DETAILED DESCRIPTION OF THE INVENTION

Molecular Sieve Used for Feedstock Pretreatment

Molecular sieves are porous solids having pores of different sizesincluding crystalline molecular sieves such as zeolites, as well ascarbons and oxides. The most commercially useful molecular sieves forthe petroleum and petrochemical industries are crystalline molecularsieves. Crystalline molecular sieves in general have a one-, two-, orthree-dimensional crystalline pore structure having uniformly sizedpores of molecular scale within each dimension. These pores selectivelyadsorb molecules that can enter the pores and exclude those moleculesthat are too large.

Aluminosilicate molecular sieves, also known as zeolites, contain athree-dimensional microporous crystalline framework structure of [SiO₄]and [AlO₄] corner sharing tetrahedral units. Zeolites are generallysynthesized by the hydrothermal crystallization of a reaction mixture ofsilicon and aluminum sources. Other metallosilicate molecular sieveswith various metals (such as, for example, gallium, iron, and/or boron)substituted for aluminum in some portion of the crystalline frameworkare also known in the art.

Molecular sieves are often formed into molecular sieve catalystcompositions to improve their durability and to facilitate handling incommercial conversion processes. These molecular sieve catalystcompositions are formed by combining a molecular sieve with a matrixmaterial and/or a binder. Although the use of binders and matrixmaterials are known for use with molecular sieves to form molecularsieve catalyst compositions, these binders and matrix materialstypically only serve to provide desired physical characteristics to thecatalyst composition and have little to no effect on conversion andselectivity of the molecular sieve.

Preferably, the feedstock is at least partially dehydrated prior topretreatment. While the molecular sieves employed in the pretreatmentsteps would be capable of dehydration, capacity for adsorption ofimpurities would be reduced if significant quantities of water areadsorbed by the molecular sieve pretreatment material. It is known inthe art that drying a hydrocarbon feedstock before pretreating with amolecular sieve having a high Si/Al ratio results in better adsorptionof polar compounds. Optimally, the feedstock would be substantiallydehydrated prior to pretreatment, with water content on the order of 100to 200 ppmw or less. This dehydration can be accomplished by any ofvarious methods known in the art, including the use of a separatemolecular sieve dehydration step.

In one embodiment of this invention, the first pretreatment step uses amolecular sieve having a Si/Al (silicon-to-aluminum) molar ratio of lessthan about 5, preferably less than about 2, more preferably betweenabout 1 and about 2. Examples of suitable molecular sieves are Lindetype A (LTA) molecular sieves, such as 3A, 4A and 5A, and Linde type X(FAU) molecular sieves such as 13X molecular sieves, and combinationsthereof. A description of these molecular sieves, their structures,properties, and methods of synthesis can be found in “Zeolite MolecularSieves,” Donald W. Breck, John Wiley & Sons, 1974, incorporated hereinby reference.

The second pretreatment step uses a molecular sieve having a Si/Al molarratio of greater than about 5, preferably greater than about 10.Suitable molecular sieves include MCM-22, MCM-36, MCM-49, MCM-56, ITQ-1,ITQ-2, PSH-3, SSZ-25, zeolite beta, mordenite, zeolite omega, US-Y,ZSM-5, and combinations thereof.

The entire contents of U.S. Pat. No. 4,954,325, teaching MCM-22; U.S.Pat. No. 5,250,277, teaching MCM-36; U.S. Pat. No. 5,236,575, teachingMCM-49; U.S. Pat. No. 5,362,697, teaching MCM-56; U.S. Pat. No.6,077,498, teaching ITQ-1; U.S. Pat. No. 6,231,751, teaching ITQ-2; U.S.Pat. No. 4,439,409, teaching PSH-3; U.S. Pat. No. 4,826,667, teachingSSZ-25; U.S. Pat. No. 3,308,069, teaching zeolite beta; U.S. Pat. Nos.3,130,007 and 4,459,426 and 4,798,816, teaching zeolite Y and itsmodified forms, such as US-Y; and U.S. Pat. No. 3,702,886, teachingZSM-5, are incorporated herein by reference. Descriptions of zeoliteomega and mordenite are referenced in the “Atlas of Zeolite FrameworkTypes,” 5th edition, Ch. Baerlocher, W. M. Meier & D. H. Olson,Amsterdam: Elsevier (2001), incorporated herein by reference. Preferredmolecular sieves for use in the second pretreatment step include thosehaving an X-ray diffraction pattern including the following d-spacingmaxima 12.4±0.25, 6.9±0.15, 3.57±0.07, and 3.42±0.07.

In another embodiment of this invention, the first molecular sieve has aSi/Al molar ratio of greater than about 5, preferably greater than about10, and most preferably is MCM-22. The second molecular sieve has aSi/Al molar ratio of less than about 5, preferably between about 1 andabout 2, and most preferably is 13X molecular sieve.

In still another embodiment of this invention, a hydrocarbon feedstockis contacted with at least two molecular sieve materials havingdifferent pore sizes. Preferably, the first molecular sieve has 12-ringpores (i.e., containing 12 T atoms) with a diameter of at least about 6Angstroms. Suitable molecular sieves having pore sizes of at least about6 Angstroms are MCM-22, MCM-36, MCM-49, MCM-56, ITQ-1, ITQ-2, PSH-3,SSZ-25, zeolite beta, mordenite, zeolite omega, US-Y, Linde type X (FAU)molecular sieves, such as 13X, and combinations thereof. Preferably, thesecond molecular sieve has pores with a diameter of less than about 6Angstroms. Suitable molecular sieves having pores with diameters of lessthan about 6 Angstroms include 10-ring pore zeolites such as ZSM-5 andother such medium pore molecular sieves as well as Linde type A (LTA)molecular sieves, such as 3A, 4A, 5A, and combinations thereof.

In still yet another embodiment, the hydrocarbon feedstock is contactedwith a first molecular sieve having pores with a diameter of less thanabout 6 Angstroms, and then a second molecular sieve having pores with adiameter of at least about 6 Angstroms. Suitable molecular sieves havingpores with diameters of less than about 6 Angstroms include 10-ring porezeolites such as ZSM-5 and other such medium pore molecular sieves aswell as Linde type A (LTA) molecular sieves, such as 3A, 4A, 5A, andcombinations thereof. Suitable molecular sieves having pore sizes of atleast about 6 Angstroms are MCM-22, MCM-36, MCM-49, MCM-56, ITQ-1,ITQ-2, PSH-3, SSZ-25, zeolite beta, mordenite, zeolite omega, US-Y,Linde type X (FAU) molecular sieves, such as 13X, and combinationsthereof.

In general, molecular sieves preferred for liquid phase pretreatment ineither of the pretreatment steps would contain 10-ring pores or larger.

Alpha value is often used as an indicator of the surface acid siteactivity of a particular molecular sieve. In general, Alpha value tendsto increase with increased framework alumina content.

The Si/Al molar ratio referred to may be determined by conventionalanalysis. This ratio is meant to represent, as closely as possible, theratio in the rigid anionic framework of the molecular sieve crystal andto exclude aluminum in the binder or in cationic or other form withinthe channels. Although molecular sieves with Si/Al molar ratios of atleast about 5 are useful for the second pretreatment step, it ispreferred to use molecular sieves having Si/Al molar ratios greater thanabout 100.

When synthesized in the alkali metal form, the molecular sieve can beconveniently converted to the hydrogen form, generally by intermediateformation of the ammonium form as a result of ammonium ion exchange andcalcination of the ammonium form to yield the hydrogen form. In additionto the hydrogen form, other forms of the molecular sieve wherein theoriginal alkali metal has been reduced, preferably to less than about1.5 percent by weight, may be used. Thus, the original alkali metal ofthe molecular sieve may be replaced by ion exchange with other suitablemetal cations of Groups I through VIII of the Periodic Table, including,by way of example, nickel, copper, zinc, palladium, calcium, or rareearth metals.

It may be useful to incorporate the above-described crystallinemolecular sieve with a matrix comprising another material resistant tothe temperature and other conditions employed in the process. Usefulmatrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay, silica, and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Naturally occurring clays which can be composited with themolecular sieve include those of the montmorillonite and kaolinfamilies, which families include the sub-bentonites and the kaolinscommonly known as Dixie, McNamee-Georgia, and Florida clays or others inwhich the main mineral constituent is halloysite, kaolinite, dickite,nacrite, or anauxite. Such clays can be used in the raw state asoriginally mined or initially subjected to calcination, acid treatment,or chemical modification.

In addition to the foregoing materials, the molecular sieves employedherein may be composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia, and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of molecular sievecomponent and inorganic oxide gel matrix, on an anhydrous basis, mayvary widely with the molecular sieve content ranging from between about1 to about 99 percent by weight and more usually in the range of about 5to about 80 percent by weight of the dry composite.

In general, although it is preferred to conduct the pretreating steps ina flow system, wherein the sorbent particles are in the form of a fixedbed of 1/16 inch to ¼ inch extrudate or pellets, other sorbent shapesand sizes or modes of contact may be employed. The precise conditionsselected for the first pretreatment step will be determined by variousconsiderations, including the nature of the feed and the desired degreeof refinement, the latter being judged from the observed catalyticconsequences of the pretreatment.

It will be obvious to one skilled in the art that parallel or seriessets of pretreating units may be used to avoid any need to shut down theprocess while regenerating or replacing one or both of the pretreatmentmolecular sieves.

A preferred embodiment of this invention employs spent catalyst foreither or both of the pretreatment steps described herein. The term“spent” as used herein will be understood to refer to a molecular sievewhich has been used as a catalyst and is no longer being used forcatalysis. A spent catalyst will usually be a molecular sieve which hasbeen used and regenerated with a subsequent loss of selectivity and/oractivity. Spent catalysts may also include used catalysts which havebeen replaced for any other reason.

Highly siliceous molecular sieves tend to have an overall lower capacityfor adsorption of polar compounds than the same structure containingmore framework alumina. In addition, a more highly siliceous molecularsieve will generally show a greater loss of adsorption capacity in thepresence of a “wet” as opposed to “dry” hydrocarbon feed. On the otherhand, molecular sieves containing higher levels of alumina in theirframework structures tend to have higher adsorption capacities and bemore hydrophilic than the highly siliceous materials. Therefore, such amolecular sieve will tend to exhibit a higher capacity for adsorption ofpolar compounds. When a high alumina content molecular sieve is used asan adsorbent with wet hydrocarbon feeds, it will tend to retain more ofits dry adsorption capacity. These arguments hold for similar structuresin which we can vary the framework alumina content substantially—aprinciple example is the faujasite structure (FAU) for which 13Xmolecular sieve represents a high alumina content example and for whichUS-Y represents a highly siliceous example.

The effect of water on the capacity of all hydrophobic molecular sieveswould teach the use of montmorillonite clays as a good choice foradsorbing highly polar compounds from water saturated hydrocarbon feeds.These clays, however, are very weak acids and the potential contaminantmust be highly polar in order to be captured on this acid clay. In fact,water saturated hydrocarbon streams are routinely treated over clay toremove strongly basic nitrogen compounds prior to their use in manypetrochemical processes.

For reactions that occur at higher temperature in the vapor phase, evenhighly polar nitrogen compounds will exhibit an adsorption/desorptionequilibrium under reaction conditions. In the vapor phase alkylation ofbenzene with ethylene above about 375° C., as much as 10 ppmw of ammoniacan be tolerated in the feed. Even though this level of feed ammoniaaffects catalyst activity, a lower steady state level of activity isreached and ethylbenzene (EB) can be produced at commercial conditions.Ammonia is a highly polar and basic nitrogen compound, although it isalso highly volatile. Since many petrochemical processes run at highertemperatures, it has become common practice to measure the level ofbasic nitrogen compounds by titration and to control these materials tohelp manage catalyst activity. If such a strong basic nitrogen compoundwere present during the liquid-phase alkylation of benzene with ethyleneto make ethylbenzene which occurs at much lower temperatures (about 200°C.), it would theoretically be adsorbed on the active sites of thecatalyst until the reaction of benzene and ethylene was essentially cutoff. In fact, there are a variety of nitrogen compounds with widelyvarying polarities and basicities. The stronger bases are detected bythe titration method discussed above, but the weaker bases are not. Withthe new lower temperature liquid phase processes, even very low levelsof strongly basic nitrogen compounds can have a material impact oncatalyst activity over time. In addition, less polar and less basicnitrogen compounds can also impact catalyst activity at lower reactiontemperatures exhibiting adsorption/desorption behavior very much likethe stronger nitrogen bases at much higher temperatures.

The use of two molecular sieves in series as described above issurprisingly effective for adsorption of a range of polar compounds, andused together can substantially enhance the cycle length for thepretreating system while providing maximum protection for the catalystsused in low-temperature, liquid-phase processing of chemical feedstocks.For example, by choosing to pretreat the feedstock over a “morehydrophilic” lower Si/Al molar ratio molecular sieve in the firstinstance, and then a “more hydrophobic” higher Si/Al molar ratiomolecular sieve in the second instance, removal of a full range ofnitrogen compounds can be accomplished, and the high efficiency of thepretreating system to remove even trace levels of these contaminants canbe maintained for extended periods.

Alkylation of Aromatic Hydrocarbons

In a further embodiment of the improved alkylation process of theinvention, at least one alkylatable aromatic compound, such as benzene,is contacted with a first pretreatment molecular sieve and a secondpretreatment molecular sieve as described herein. The treatedalkylatable aromatic compound and at least one alkylating agent arecontacted under sufficient reaction conditions (preferably liquid phase)and in the presence of a catalyst to provide an alkylated aromaticproduct comprising at least one alkyl group derived from said alkylatingagent. Preferably, a benzene feedstock is contacted with a firstmolecular sieve, such as 13X molecular sieve, and a second molecularsieve, such as MCM-22, to produce a treated benzene feedstock stream.The treated benzene feedstock stream is contacted with ethylene in thepresence of an alkylation catalyst, such as MCM-22, MCM-36, MCM-49 orMCM-56, under suitable alkylation conditions to form ethylbenzene.Optionally, an alkylating agent, such as ethylene, may be contacted withone or more molecular sieves, such as the first and/or secondpretreatment molecular sieves, as described herein to form a treatedalkylating agent. Often at least one polyalkylated aromatic compound isalso produced. Then at least a portion of the polyalkylated aromaticcompound(s) and at least one alkylatable aromatic compound can becontacted under sufficient reaction conditions (preferably liquid phase)in a transalkylation section in the presence of a catalyst to convert atleast a portion of the polyalkylated aromatic compound(s) to amonoalkylated aromatic compound.

Most aromatic alkylation processes having a liquid phase transalkylationstep are suitable for the improvement in accordance with the process ofthe present invention by the addition of a pretreatment step asdescribed above. For example, U.S. Pat. Nos. 4,962,256; 4,992,606;4,954,663; 5,001,295; and 5,043,501, each of which are incorporatedherein by reference in their entirety for the purpose of describingparticular alkylation processes, describe alkylation of aromaticcompounds with various alkylating agents over catalysts comprising aparticular crystalline material, such as PSH-3 or MCM-22. U.S. Pat. No.4,962,256 describes preparing long chain alkylaromatic compounds byalkylating an aromatic compound with a long chain alkylating agent. U.S.Pat. No. 4,992,606 describes preparing short chain alkylaromatics byalkylating an aromatic compound with a short chain alkylating agent.U.S. Pat. No. 4,954,663 teaches alkylation of phenols, and U.S. Pat. No.5,001,295 teaches alkylation of naphthalene. U.S. Pat. No. 5,043,501describes preparation of 2,6-dimethylnaphthalene. These are a fewexamples, although certainly not an exhaustive listing, of the types ofalkylation processes which may be improved with the present invention.

The term “aromatic” in reference to the alkylatable compounds which areuseful herein is to be understood in accordance with its art-recognizedscope which includes alkyl substituted and unsubstituted mono- andpolynuclear compounds. Compounds of an aromatic character which possessa heteroatom (e.g., N or S) are also useful provided they do not act ascatalyst poisons under the reaction conditions selected.

Substituted aromatic compounds which can be alkylated herein mustpossess at least one hydrogen atom directly bonded to the aromaticnucleus. The aromatic rings can be substituted with one or more alkyl,aryl, alkaryl, alkoxy, aryloxy, cycloalkyl, halide, and/or other groupswhich do not interfere with the alkylation reaction.

Suitable aromatic hydrocarbons include benzene, naphthalene, anthracene,naphthacene, perylene, coronene, and phenanthrene.

Generally the alkyl groups which can be present as substituents on thearomatic compound contain from 1 to about 22 carbon atoms and preferablyfrom about 1 to 8 carbon atoms, and most preferably from about 1 to 4carbon atoms.

Suitable alkyl substituted aromatic compounds include toluene; xylene;isopropylbenzene; normal propylbenzene; alpha-methylnaphthalene;ethylbenzene; cumene; mesitylene; durene; p-cymene; butylbenzene;pseudocumene; o-diethylbenzene; m-diethylbenzene; p-diethylbenzene;isoamylbenzene; isohexylbenzene; pentaethylbenzene; pentamethylbenzene;1,2,3,4-tetraethylbenzene; 1,2,3,5-tetramethylbenzene;1,2,4-triethylbenzene; 1,2,3-trimethylbenzene, m-butyltoluene;p-butyltoluene; 3,5-diethyltoluene; o-ethyltoluene; p-ethyltoluene;m-propyltoluene; 4-ethyl-m-xylene; dimethylnaphthalenes;ethylnaphthalene; 2,3-dimethylanthracene; 9-ethylanthracene;2-methylanthracene; o-methylanthracene; 9,10-dimethylphenanthrene; and3-methyl-phenanthrene. Higher molecular weight alkylaromatichydrocarbons can also be used as starting materials and include aromatichydrocarbons such as are produced by the alkylation of aromatichydrocarbons with olefin oligomers. Such products are frequentlyreferred to in the art as alkylate and include hexylbenzene,nonylbenzene, dodecylbenzene, pentadecylbenzene, hexyltoluene,nonyltoluene, dodecyltoluene, pentadecytoluene, etc. Very often alkylateis obtained as a high boiling fraction in which the alkyl group attachedto the aromatic nucleus varies in size from about C₆ to about C₁₂.Reformate, especially reformate containing substantial quantities ofbenzene, toluene, and/or xylene, would also constitute a useful feed forthe alkylation process of this invention.

The alkylating agents which are useful in the process of this inventiongenerally include any aliphatic or aromatic organic compound having oneor more available alkylating aliphatic groups capable of reaction withthe alkylatable aromatic compound, preferably with the alkylating grouppossessing from 1 to 5 carbon atoms. Examples of suitable alkylatingagents are olefins such as ethylene, propylene, the butenes, and thepentenes; alcohols (inclusive of monoalcohols, dialcohols, trialcohols,etc.) such as methanol, ethanol, the propanols, the butanols, and thepentanols; aldehydes such as formaldehyde, acetaldehyde,propionaldehyde, butyraldehyde, and n-valeraldehyde; and alkyl halidessuch as methyl chloride, ethyl chloride, the propyl chlorides, the butylchlorides, and the pentyl chlorides, and so forth.

Mixtures of light olefins can also be useful as alkylating agents in thealkylation process of this invention. Accordingly, mixtures of ethylene,propylene, butenes, and/or pentenes which are major constituents of avariety of refinery streams, e.g., fuel gas, gas plant off-gascontaining ethylene, propylene, etc., naphtha cracker off-gas containinglight olefins, refinery FCC propane/propylene streams, etc., are usefulalkylating agents herein.

Typical aromatic alkylation reactions which may be improved the presentinvention include obtaining ethylbenzene from the reaction of benzenewith ethylene, cumene from the reaction of benzene with propylene,ethyltoluene from the reaction of toluene with ethylene, and cymenesfrom the reaction of toluene with propylene.

The alkylation process of this invention is conducted such that theorganic reactants, i.e., the alkylatable aromatic compound and thealkylating agent, are brought into contact with an alkylation catalystin a suitable reaction zone such as, for example, in a flow reactorcontaining a fixed bed of the catalyst composition, under effectivealkylation conditions. Such conditions include a temperature of fromabout 0° C. to about 500° C., and preferably between about 50° C. andabout 250° C.; a pressure of from about 0.2 to about 250 atmospheres;and preferably from about 5 to about 100 atmospheres, a molar ratio ofalkylatable aromatic compound to alkylating agent of from about 0.1:1 toabout 50:1, and preferably can be from about 0.5:1 to about 10:1; and afeed weight hourly space velocity (WHSV) of between about 0.1 and 500hr⁻¹, preferably between 0.5 and 100 hr⁻¹.

The reactants can be in either the vapor phase or the liquid phase andcan be neat, i.e., free from intentional admixture or dilution withother material, or they can be brought into contact with the zeolitecatalyst composition with the aid of carrier gases or diluents such as,for example, hydrogen or nitrogen.

When benzene is alkylated with ethylene to produce ethylbenzene, thealkylation reaction may be carried out in the liquid phase. Suitableliquid phase conditions include a temperature between 300° and 600° F.(about 150° and 316° C.), preferably between 400° F. and 500° F. (about205° C. and 260° C.); a pressure up to about 3000 psig (20875 kPa);preferably between 400 and 800 psig (2860 and 5600 kPa), a spacevelocity between about 0.1 and 20 WHSV, preferably between 1 and 6 WHSV,based on the ethylene feed; and a ratio of the benzene to the ethylenein the alkylation reactor from 1:1 to 30:1 molar, preferably from about1:1 to 10:1 molar.

When benzene is alkylated with propylene to produce cumene, the reactionmay also take place under liquid phase conditions including atemperature of up to about 250° C., e.g., up to about 150° C., e.g.,from about 10C to about 125° C.; a pressure of about 250 atmospheres orless, e.g., from about 1 to about 30 atmospheres; and an aromatichydrocarbon weight hourly space velocity (WHSV) of from about 0.1 hr⁻¹to about 250 hr⁻¹, preferably from 1 hr⁻¹ to 50 hr⁻¹.

The aromatic feedstock stream may contain impurities such as, forexample, olefins, diolefins, styrene, oxygenated organic compounds,sulfur containing compounds, nitrogen containing compounds, oligomericcompounds, and combinations thereof. These impurities or contaminantscan deactivate or plug alkylation and/or transalkylation catalysts.These impurities may originate from external feed streams or may beproduced in either liquid or vapor phase alkylation reactors, or theymay come from both of these sources.

In the process of the present invention these impurities are removedthrough staged adsorption in a pretreatment step. The removal of theseimpurities extends the cycle time between catalyst changeouts bypreventing poisoning and potential plugging of the valuable catalysts.The operating conditions of the pretreatment step are such that the feedis in the liquid phase.

In some embodiments of the invention, the feedstock stream to bepretreated, i.e. the alkylatable aromatic compound and optionally, thealkylating agent, one or more of which contain some or all of theabove-referenced impurities, are brought into contact with the first andsecond pretreatment molecular sieves, respectively, in a suitablepretreatment zone such as, for example, in a flow reactor containing afixed bed comprising the molecular sieve, under effective liquid phaseconditions to effect the removal of the impurities by adsorption. Thealkylatable aromatic hydrocarbon and the alkylating agent may becontacted with the first and/or second pretreatment molecular sieveseither sequentially or concurrently. The preferred conditions employedin the pretreatment steps include a temperature of from about 70° F. toabout 600° F., and preferably between about 150° F. and about 500° F.; aweight hourly space velocity (WHSV) of between about 0.1 hr⁻¹ and about200 hr⁻¹, and preferably from 0.5 hr⁻¹ to about 100 hr⁻¹; and a pressurebetween about ambient and about 600 psig. Operating conditions for thepretreatment steps can be any conditions that are appropriate to achievethe preferred inlet conditions for the alkylation reaction.

EXAMPLES

The following examples provide an illustration of the effectiveness ofthe present invention for alkylation of an aromatic hydrocarbon. Abenzene feed was contacted with a conventional 13X molecular sieve in anupflow pretreatment unit. The treated benzene feed and untreatedethylene were contacted with an alkylation catalyst in a reactor undersuitable liquid phase alkylation conditions to produce ethylbenzene. Theactivity of the alkylation catalyst declined by 38 percent after beingon stream for 22 days when the benzene feed was pretreated with 13Xmolecular sieve. Subsequently, an approximately equal volume of 4Amolecular sieve was added to the top of the pretreatment unit anddownstream from the 13X molecular sieve. After the addition of the 4Amolecular sieve, the reactor remained in service using the samealkylation catalyst with no interim regeneration procedures. Thepretreatment of the benzene feed with 13X molecular sieve and 4Amolecular sieve followed by the alkylation of benzene with ethylenecontinued to be operated at substantially the same operating conditionsfor another 22 days. During this time, the activity of the alkylationcatalyst showed a further decline of only 2 percent over the second 22day period, for a total reduction of 40 percent from the initialcatalytic alkylation activity. This experiment reveals a substantial andeconomically significant reduction in the rate of catalyst aging.

In a prophetic experiment comparable to that above, an approximatelyequal volume of MCM-22 would be placed in a pretreatment unit downstreamof 13X molecular sieve. The reactor would remain in service and beoperated with no interim regeneration procedures. It is expected thatduring a test of 22 days in duration, the activity of the alkylationcatalyst would show no additional decline. This experiment is expectedto reveal a substantial and economically significant reduction in therate of catalyst aging.

It will be recognized by those skilled in the art that additionalpretreatment steps can be combined with the pretreatment processdescribed above, and such combinations are considered to be within thescope of this invention.

1. A process for alkylation of an aromatic hydrocarbon stream comprisingimpurities in which said impurities are removed in a pretreatment systemhaving a first stage, a second stage located downstream of said firststage and a cycle length, said process comprising the steps of: (a)contacting the aromatic hydrocarbon stream with a first molecular sievewhich is 13X in said first stage of said pretreatment system, to removeat least a portion of said impurities, to produce a partially treatedaromatic hydrocarbon stream; (b) contacting said partially treatedaromatic hydrocarbon stream with a second molecular sieve which is 4A ina second stage of said pretreatment system to remove substantially allof the remaining portion of said impurities, and to produce a fullytreated aromatic hydrocarbon stream; and (c) contacting said fullytreated aromatic hydrocarbon stream with an alkylating agent in thepresence of an alkylation catalyst and under alkylation conditions, toproduce an alkylated aromatic hydrocarbon stream; and wherein said cyclelength of said pretreatment system is greater than said cycle lengthusing said first stage of said pretreatment system alone or said secondstage of said pretreatment system alone.
 2. The process of claim 1,further comprising the step of contacting said alkylating agent of step(c) with a third molecular sieve, to produce a treated alkylating agent,and contacting said treated alkylating agent with said treated aromatichydrocarbon stream of step (b), to produce said alkylated aromatichydrocarbon stream of stop (c).
 3. The process of claim 1, wherein thefirst molecular sieve has a Si/Al molar ratio of less than about 5 andthe second molecular sieve has a Si/Al molar ratio of greater than about5.
 4. The process of claim 1, wherein the first molecular sieve has aSi/Al molar ratio of less than about
 2. 5. The process of claim 1,wherein the second molecular sieve further comprises a molecular sieveselected from the group consisting of MCM-22, MCM-36, MCM-49, MCM-56,ITQ-1, ITQ-2, PSH-3, SSZ-25, zeolite beta, mordenite, zeolite omega,US-Y, ZSM-5, and combinations thereof, any of which may be a spentcatalyst.
 6. The process of claim 1, wherein the first molecular sievefurther comprises a molecular sieve selected from the group consistingof MCM-22, MCM-36, MCM-49, MCM-56, ITQ-1, ITQ-2, PSH-3, SSZ-25, zeolitebeta, mordenite, zeolite omega. US-Y, and combinations thereof, any ofwhich may be a spent catalyst.
 7. The process of claim 1, wherein thearomatic hydrocarbon is benzene or toluene and wherein the alkylatingagent is ethylene or propylene.